Anorexia Nervosa (AN) is a serious psychiatric illness with the highest mortality rate of any other psychiatric disorder. There is no established efficacious treatment for adult AN. Promising outcomes are seen in family- based treatment (FBT) for adolescents. FBT has undergone significant development in the past 10 years;delivered in conjoint and separated format, manualized for adolescent AN, dosage requirements investigated, adapted and manualized for adolescent bulimia nervosa and evaluated for older adolescents. Given the success of FBT with adolescents and high treatment retention rates for this age group, the absence of FBT for young adults with AN is surprising given the comparable dependence upon family between late adolescence and young adulthood. Our preliminary findings suggest that enlisting the family in treatment for this older age group may be efficacious. This is a proposal for a Stage I treatment development program to develop and test FBT to promote weight restoration in young adults (18-25 yrs) with AN (FBT-Y). Important adaptations of 6- month, 18 session FBT-Y are these. First, broadening the notion of family of origin (parents) to also include family of 'choice'(e.g., spouse/cohabiting partner, aunts/uncles, grandparent/s), i.e., adult family members who have an emotional investment in the patient, which may include emotional (e.g. marriage) and/or financial leverage (e.g., paying college tuition, rent, etc., for the patient). Second, FBT-Y fosters collaboration between the young adult and the family of choice;and third, FBT-Y addresses in an up-to-date way young adult developmental concerns. This study involves 2 Phases. Phase 1 is to develop and refine the FBT-Y manual, utilizing an iterative case series approach, using initial and ongoing meetings of the expert treatment development team, video-taping and analysis of sessions, weekly case conferences, and on-going assessments of patient, family and therapist. These assessments will be used to make necessary changes to the treatment manual. Up to two case series of 5 patients each will be utilized to develop the manual. Phase 2 of the study will assess the feasibility, acceptability and preliminary efficacy of FBT-Y using an open trial (n=20). Feasibility and acceptability will be assessed using questionnaires and qualitative interviews and examining recruitment and dropout rates. Effect-size and effect-size variability estimates of FBT-Y on our primary outcome measure, i.e., body mass index will be assessed. In addition, exploratory outcome examining secondary AN symptoms and psychosocial functioning will be examined. These calculations will inform a future full-scale clinical trial. PUBLIC HEALTH RELEVANCE: Anorexia Nervosa (AN) has the highest mortality rate compared to any other psychiatric disorder, yet there is no established treatment for adult AN. The most promising treatment is family-based treatment for adolescents with AN. The current study is to refine and test an approach developed form family-based treatment, family-based treatment for weight restoration in young adults (18-25 years) with AN.